Effect of systemic antimicrobial prophylaxis on microbial flora

Fifteen patients undergoing intensive chemotherapy for oat cell carcinoma of the lung in a protected environmental unit received antimicrobial prophylaxis with oral trimethoprim-sulfamethoxazole and short courses of parenteral ticarcillin, tobramycin, and miconazole. Altogether, 58 (65%) of 89 strains of aerobic bacteria and 28 (60%) of 47 strains of anaerobic bacteria present before prophylaxis were no longer cultured from stool specimens during prophylaxis. Ten strains of bacteria and four fungi were acquired in the stools during prophylaxis. Most fungi persisted in the throat and stools during prophylaxis. Bacterial infections occurred infrequently, but three patients developed Candida esophagitis. The regimen was well tolerated with minimal side effects.